Diagnostic Aids

The scan tester reads engine temperature in degrees centigrade. After engine is started, temperature should rise steadily to about 194°F (90°C), then stabilize when thermostat opens.

When a Code 15 is set, ECM will turn on engine cooling fan.

Code 15 will set if signal wire or ground wire is open. If Code 15 is intermittent, see INTERMITTENTS in TESTS W/O CODES article in this section.

Fig 1: Code 15 Schematic - Coolant Temp. Sensor (Temp. Too Low)

Courtesy of GENERAL MOTORS CORP.

Fig 2: Code 15 Flow Chart - Coolant Temp. Sensor (Temp. Too Low)

Courtesy of GENERAL MOTORS CORP.